This invention relates to a walking beam scroll saw or jigsaw.
Generally, a walking beam scroll saw or jigsaw utilizes two parallel arms or beams and a relatively thin under blade tension between the outer ends of the beams. The beams are pivotally mounted on trunnions or bearings, and means are employed at the ends of the beams opposite the blade so as to maintain the blade under tension. A motor or other drive means is connected to one of the beams (conventionally at the end thereof toward the blade) so as to reciprocate the beams in an up and down fashion such that the saw blade reciprocates relative to the workpiece for cutting purposes. Walking beam saws generally have the same uses for cutting wood, metal, plastic, and other materials, as a band saw, but the walking beam saw blades may be replaced in a relatively short time and at low expense, as compared to a band saw. Also, like a band saw, walking beam saws may be used to cut curvilinear lines and rather intricate patterns and shapes.
As is typical in most reciprocal saws, the teeth on the saw blade are angled such that the saw blade cuts primarily on the downstroke. Such walking beam saws are well known.
Reference may be made to U.S. Pat. No. 3,878,876 in which a suspension arrangement for a walking beam saw is disclosed. In this '876 patent, the saw blade is floatingly supported in a frame utilizing forked clamping elements which are clamped to the ends of the saw blade. The forked elements holding the blade fit into a depression fulcrum arrangement on the end of the arm so that the blade can rock or tilt.
Heretofore, bevel or angle cuts made with a walking beam saw were achieved by angling the work supporting table relative to the vertical plane of the reciprocating blade. However, with the work mounted at an angle, it was sometimes difficult for the saw operator to hold the wood against slipping on the angled table to achieve accurate cutting results.
Also, other prior scroll saws or jigsaws were known in which a reciprocating blade was maintained under tension and reciprocated up and down by means of a crank drive or the like. Typically, these prior art jigsaws utilized a spring loaded mechanism for returning the blade from its lowered position to its raised position for being forcefully drawn down by the drive mechanism during its cutting stroke. However, when cutting certain types of material which may frictionally grip the sides of the blade, since the blade was not forcefully drawn to its raised position, compression loads with consequent bending could be applied to the blade causing blade breakage or bending if the spring return could not move the blade to its raised position.
In certain prior art walking beam scroll or jigsaws, the beams were made of elongate plate-like members on edge relative to their pivot axis so as to have substantial rigidity in vertical direction. However, because the beams of these walking beam scroll saws were relatively thin in lateral direction, such scroll saws may not have the capability of having high lateral loads applied thereto, such as may be experienced in cutting tight radii in an intricate scroll workpiece, or in making long, lateral rip cuts. To overcome this, frictional bearing plates were often provided to prevent lateral displacement of the beams, but these friction plates reduced cutting efficiency. Moreover, such walking beam saws, even with the lateral friction plates, were not completely satisfactory when ripping relatively long workpieces with the blade positioned laterally with respect to the reciprocating movement of the walking beams.
In other prior art walking beam saws, the beams were made of complex castings so as to be rigid in both vertical and lateral directions. However, these cast beams incorporated a substantial mass which, in turn, increased vibration during operation or required a reduction in operating speed.